P54. New electrodes for routine intra-operative dual near-field (DNF) monitoring of the cochlear nerve. Issue 8 (August 2015)

• Record Type: Journal Article
• Authors: Rosahl, S.; Lehmberg, J.; Krieg, S.; Gerlach, R.; Scheiwe, C.
• Is Part Of: Clinical neurophysiology. Volume 126:Issue 8(2015:Aug.)
• Page Start: e121
• Page End: 1047
• Publication Date: 2015-08
• Subjects: Neurophysiology -- Periodicals; Electroencephalography -- Periodicals; Electromyography -- Periodicals; Neurology -- Periodicals; 612.8
• DOI: 10.1016/j.clinph.2015.04.189
• Languages: English
• ISSNs: 1388-2457

Abstract

<abstract xml:lang="en" abstract-type="author" id="ab005"> <title> <x xml:space="preserve">Abstract</x> </title> <sec> <title id="st005">Purpose</title> <p id="sp005">Intraoperative near-field recording of cochlear and brainstem auditory potentials (BAEP) can significantly reduce acquisition time (<xref id="c0005" rid="b0010">Matthies and Samii, 1997</xref>; <xref id="c0010" rid="b0015">Moller et al., 1994</xref>). Over a period of 15 years we have designed and tested tympanic and brainstem electrodes to monitor the functional integrity of the lower auditory pathway (cochlea, cochlear nerve, brain stem) during surgery in the cerebello-pontine angle (CPA) and the internal auditory canal.</p> </sec> <sec> <title id="st010">Method</title> <p id="sp010">For routine application, a ball-shaped design has proven to be most advantageous and was developed with a company (inomed Medizintechnik, Emmendingen, Germany). Currently, two stainless steel mini-ball electrodes are employed. One of them is connected to a stainless-steel spring reaching out of an insert earphone and attaches to the tympanic membrane (ECoG, <xref id="c0015" rid="b0005">Krieg et al., 2014</xref>). A second mini-ball electrode with a diameter of 1.6 mm can be placed on the cochlear nerve or at the dorsal cochlear nucleus of the brainstem to record a central auditory brainstem response (CABR). These electrodes were applied in more than 500 patients with lesions in the CPA and internal auditory canal during microsurgery. Near-field potentials have been compared to the far-field auditory brainstem response (ABR, Cz-A1/A2, band-pass 100–3000 Hz). Click stimuli were applied at 13.2 Hz. Data processing was carried out with a commercially available electrophysiological monitoring system (ISIS®, inomed).</p> </sec> <sec> <title id="st015">Results</title> <p id="sp015">Electrode impedance was consistently lower than 5 kOhm at 1 kHz. Because of its ball shape, the intracranial electrode could easily be placed in the lateral recess of the fourth ventricle (dorsal cochlear nucleus, DCN) and on the cochlear nerve without having to pay attention to a specific contact area on its surface (<xref id="c0020" rid="f0005">Fig. 1</xref>). If necessary, it was slid out just as easy.</p> <p id="sp020">Waves I and II of the BAEP were best identified in recordings at the tympanic membrane, wave III to V were largest in recordings with the mini-ball electrodes at the brainstem or on the cochlear nerve. Compared to far-field ABR, amplitudes were 3–4 times larger for ECoG, and 2–20 times larger for CABR in patients with functional hearing (<xref id="c0025" rid="f0010">Fig. 2</xref>). CABR was more variable than the ECoG, depending mostly on electrode location relative to the brainstem generators. With optimal placement of the electrodes, reliable BAEP averages were obtained within 40 s in far-field, and within less than 10 s in near-field recordings.</p> </sec> <sec> <title id="st020">Conclusions</title> <p id="sp025">Electrodes developed for near-field recording on both ends of the cochlear nerve allow for an almost instantaneous feedback on the integrity of hearing. Dual near-field (DNF) recording is significantly superior to standard auditory far-field monitoring.</p> </sec> </abstract>